Patent Literature 1 discloses a rotor core of a superconducting rotary machine. The rotor core of the superconducting rotary machine is constituted by a substantially hollow cylindrical body which is made of a non-magnetic material and has therein a ring-shaped space axially extending therethrough. The rotor core is cooled by a helium gas flowing from a base end side of the rotor core to a terminal end side of the rotor core and the helium gas flowing from the terminal end side of the rotor core to the base end side of the rotor core.